This invention relates in general to magnetostatic wave structures and relates more particularly to the coupling between such structures. Yttrium-Iron-Garnet (YIG) devices are widely used in combination with an applied magnetic field to accomplish wide band tuning in microwave circuits. These YIG devices are typically coupled by microstrip conductors. In the case of a YIG sphere, the microstrip conductor partially encircles the sphere in order to strongly couple to the magnetic field associated with the YIG sphere. Changes in the magnetic field surrounding the YIG sphere induces in this conductor a current which is carried by the conductor to an area within the magnetic field of another YIG sphere.
In recent years, thin film YIG devices have been developed which function as resonators and delay lines. In U.S. Pat. No. 4,528,529 entitled MAGNETOSTATIC WAVE RESONATOR issued to Ernst Huijer on July 9, 1985 is presented a magnetostatic wave resonator that uses a thin rectangular film of yttrium-iron-garnet to carry the magnetostatic waves. The magnetostatic waves reflect at the ends of this YIG film to produce a resonant structure. These YIG devices also utilize microstrip conductors to convert the variations in the magnetic field near the YIG film into a current that is carried by the microstrip conductor to another device. Unfortunately, the energy transmitted from one device to another is reduced by the conduction and radiation losses of the microstrip conductors.
Magnetostatic Wave (MSW) resonators have been produced that utilize shallow etched gratings or overlying metal gratings to selectively couple to particular wavelengths of the magnetostatic waves in the resonator (See, for example, the article by J.P. Casters, et al entitled A TUNABLE MAGNETOSTATIC VOLUME WAVE OSCILLATOR in the IEEE MTT-S International Microwave Symposium Digest (1983)). Unfortunately, these structures have a very high loss and their performance is critically dependant on the etch depth and metal thickness, respectively, of the gratings. Therefore, it would be advantageous to have a low loss coupling mechanism between MSW devices.
In the article entitled COMPACT MAGNETOSTATIC WAVE CHANNELIZER by Michael R. Daniel and J. D. Adam, 1986 IEEE MTT-S International Microwave Symposium Digest, p. 481 is presented a channelizer in which a set of long rectangular blocks of yttrium iron garnet are mounted on a substrate in a parallel arrangement so that a first end of each of these blocks is located under a single input transducer. This input transducer launches magnetostatic waves in each of these blocks. Each block has it own output transducer so that this arrangement functions as a set of parallel channels for the signal input at the input transducer. A tapered magnet applies a magnetic field to these blocks that varies from one to the next so that each exhibits a different frequency response. In order to eliminate crosstalk between these blocks, magnetic shielding is located between each pair of adjacent blocks.